A wide variety of substances have been proposed for use as fat substitutes in food compositions. The chemical structures of such substances are selected such that they are more resistant to breakdown by the metabolic processes of the human digestive system which normally occur upon ingestion of conventional triglyceride lipids. Because of their increased resistance to digestion and absorption, the number of calories per gram available from the fat substitutes is considerably reduced as compared to common vegetable oils, animal fats, and other triglyceride lipids. The use of such substances thus enables the preparation of food compositions which are limited in calories derived from fat.
U.S. Pat. No. 4,861,613 describes the preparation of one class of particularly useful fat substitutes wherein a polyol such as glycerin is alkoxylated with an epoxide such as propylene oxide and then esterified with any of a number of fatty acids or equivalents thereof to form an esterified alkoxylated polyol. These substances have the physical and organoleptic properties of conventional triglyceride lipids, yet are significantly lower in available (absorbed) calories than edible oils owing to their pronounced resistance towards pancreatic lipase enzymatic hydrolysis. The thermal and oxidative stability of the esterified alkoxylated polyols renders them especially suitable for use in the preparation of reduced calorie food compositions requiring exposure to high temperatures.
Unfortunately, as a consequence of their hydrolytic stability and low digestibility, the esterified alkoxylated polyols described in U.S. Pat. No. 4,861,613 which are substantially liquid at body temperature may tend to cause certain undesirable gastrointestinal side effects when consumed at high levels in the diet. That is, since such esterified alkoxylated polyols are not readily broken down into simpler substances upon ingestion, they largely retain their oily, fat-like character and pass through the digestive tract in substantially unaltered form. Problems with diarrhea, leakage of the fat substitute through the anal sphincter (sometimes referred to as "passive oil loss"), and separation of the fat substitute as an oil from the excreted fecal matter can occur as a result of the non-digestibility of the fat substitute. Liquid fat substitutes other than esterified alkoxylated polyols which are similarly resistant towards digestion are known to produce comparable gastrointestinal side effects. Examples include sucrose polyester which is esterified with up to 8 fatty acid groups; see U.S. Pat. Nos. 3,954,976, 4,005,195, 4,005,196, and 5,006,360. Obviously, such problems will greatly limit the maximum usage level of these substances which can be tolerated in various food compositions, thereby constraining the amount of conventional triglyceride and the number of calories which can be removed from certain foods.
European Patent Publication No. 571,219 proposes the use of certain esterified propoxylated glycerin fat substitutes which have a particular distribution of fatty acids incorporated therein to achieve a minimum solids content at 27.degree. C. as a means of alleviating such gastrointestinal side effects. As a result of their relatively high solids content, however, such substances may tend to have an undesirable waxy or greasy mouthfeel, thereby limiting their utility in food products which normally require the incorporation of a liquid oil as the fat component. EP 571,219 suggests that this problem may be alleviated by combining the esterified propoxylated glycerin with a liquid triglyceride lipid; for example, fine particles of the fat substitute may be advantageously dispersed in a matrix of the liquid triglyceride lipid. Such a solution, however, is not entirely satisfactory since the caloric content of the esterified propoxylated glycerin is increased considerably by the addition of the triglyceride, which contains 9 calories per gram. That is, one can improve the organoleptic qualities of the esterified propoxylated glycerin by such blending, but at the expense of a less significant reduction in calories than would be achieved if the esterified propoxylated glycerin could be used as the sole fatty material in the food product.